A 14-year-old has been charged with murdering west Auckland dairy owner Arun Kumar, while a 13-year-old has been charged with manslaughter.

The 13-year-old's lawyer, David Niven, said a young witness who said he was with the boys on the morning had told a pack of lies.

Mr Niven said the boy repeatedly changed his story while being interviewed by police. He said the boy was only trying to save his own skin and made up stories to suit.

Flowers placed outside Mr Kumar's dairy in Henderson. Photo: RNZ

Mr Niven said the boys had only planned to break into the local shoe shop - not to hurt anyone.

He played the footage of the robbery captured on the dairy's security cameras and pointed out that as soon as the 14-year-old pulled out his knife, his client backed out of the doorway.

Mr Niven said his client never used his weapon and could not have anticipated what the other boy would do. He also said his client ran before the other boy fatally stabbed Mr Kumar.

Mr Niven also spoke of his client's brain damage, due to his mother drinking while she was pregnant. He said the boy had a low IQ and couldn't even name all the months of the year.

Critical period lasted just six seconds

The 14-year-old's lawyer, Maria Pecotic, also spoke of her client's background.

At the time of the stabbing, the boy was living in his mother's home where drugs were being sold and he had developed an addiction to synthetic cannabis.

Ms Pecotic reminded the jurors that her client had suffered a severe brain injury when he was hit by a car on a pedestrian crossing, causing a fracture to his skull.

She summed up the evidence from a neuropsychologist who found the brain injury made the boy impulsive when he was faced with complex situations.

She said the dairy was one of those situations.

Ms Pecotic said there was very little time for the boys to come up with a plan. She said, once inside, the critical period of the incident lasted just six seconds and, in that time, Mr Kumar armed himself with a steel pole and her client responded by stabbing him three times.

Ms Pecotic said, when the stabbing happened, her client was walking backwards and shortly before he made the fatal lunge, Mr Kumar had grabbed at the boy's neck and upper torso area.

Crown prosecutor Kieran Raftery told the jurors yesterday that it was Mr Kumar acting in self-defence against a knife-wielding thief in his shop.

He said no one in their right mind watching the CCTV footage would think it was the 14-year-old defending himself and that was utter rubbish.

On Monday, Justice Lang will sum up the case to the jurors before they retire to consider their verdict.